1. Field of the Invention
The present invention relates to a method of determining the mass of drops or droplets ejected from an inkjet device or dispenser, and more particularly, to a method for determining the mass of drops or droplets as well as assessing the mixing effects of solutions ejected from an inkjet dispenser utilizing UV visible spectroscopy.
2. Discussion of the Related Art
In an increasingly large number of industries, the ability to accurately and repeatedly deposit nanogram quantities of a given substance is critical to the development of new technologies. This is largely driven by a move towards micro- and nano-scale products that require extremely accurate processing steps. Many applications require repeatable deposition of nano- or picoliter quantities of solutions to precise locations on a target. This is particularly true in the manufacturing of many medical devices where the amount and location of drug loading must be controlled to very precise specifications. In such cases, drop-on-demand inkjet technology is an attractive choice as it addresses the needs for both accurate targeting and repeatable droplet ejection.
Particularly for these kinds of highly-controlled applications, the quantity of substance being ejected from the inkjet devices must be known to extreme accuracy. Various methods have been described to determine the quantity of substance, including the use of atomic force microscopy cantilevers, quartz crystal microbalances, nanomechanical resonators and gravimetry. However, all of these methods require either highly sensitive, time-consuming calibration processes that are impractical for a manufacturing process application or a large number of drops to ensure an accurate measurement. A system that can quantify the material dispensed in small drop numbers, requires little calibration and can be easily integrated into an existing process is of importance in many industries. UV-visible spectroscopy meets these criteria due to its sensitive detections limits, relatively simple calibration and short sampling time.
Despite UV-visible spectroscopy's relative weakness in identifying unknown compounds, its ability to quantify known substances in solution is quite robust. As such, it is a common choice for applications in which a known substance is dissolved in a known solvent and only determination of the concentration is desired. Further, in mixed solutions with more than one component, absorbance values measured at multiple wavelengths may be compared to determine relative concentrations of individual components, which is useful for assessments of solution mixing and degradation of individual components.
Accordingly, there exists a need for overcoming the disadvantages associated with the current technology by developing a method of determining the mass of individual and small quantities of droplets ejected from an inkjet device and a method for quantitative assessments of mixing effects of solutions dispensed from an inkjet device.